The present invention relates to a new constructive arrangement applied to a suction muffler assembly for hermetic compressors of the reciprocating type which are used in small refrigerating machines.
Hermetic refrigeration compressors of the reciprocating type consist usually of a motor-compressor unit mounted within a hermetically sealed case. These compressors are usually provided with a cylinder and a reciprocating piston, which takes in and compresses the refrigerant gas during the operation of the electric motor.
Due to the simplicity of construction, these compressors use reed type suction and discharge valves, which cause together with the piston an intermittent flow of refrigerant gas. This intermittent flow of refrigerant gas tends to cause noise, which makes necessary the provision of acoustic dampening systems including muffler assemblies mounted both in the suction and in the discharge line of the compressor.
In these compressors, the compression of the refrigerant gas generates high temperatures in the cylinder and in the cylinder head thereof, causing heat transmission to other metallic parts of the motor-compressor unit. These heated metallic parts start irradiating heat, superheating the refrigerant gas in the suction system of the compressor, causing a density decrease of the refrigerant gas which is taken into the cylinder, thus decreasing mass pumped and consequently the efficiency of the compressor.
In known compressors, this refrigerant gas superheating is almost always reduced by means of insulating plastic material suction muffler assemblies which are usually mounted away from the metallic parts of the motor-compressor unit.
These suction muffler assemblies made of plastic material having thermal insulating characteristics consist usually of a muffler body in the form of a hermetic shell mounted outside the cylinder head, having at least one internal chamber and being provided with a gas inlet opening and a gas outlet opening, the latter being tightly connected to the inlet nozzle of a body which defines, in its inside, independently or together with a portion of the cylinder head, a suction pipe that is maintained in fluid communication with the suction valve of the compressor.
Due to the complex construction of the internal portion of the muffler body, which internal portion can include several leading and deflecting means of gas flow, said muffler assembly is generally formed of two halves to be connected to each other by a tight fitting of their edges.
In the reciprocating compressors with a vertical shaft and having a pump disposed in the upper part of the case above the electric motor, the tightness of the fitting of said two parts and/or halves which form the muffler assembly is necessary to prevent the oil which is sprinkled on the cylinder head from penetrating into the muffler assembly, since this oil tends to be undesirably taken in by the cylinder of the compressor. It must be pointed out that the oil in question is the one which is being sprinkled under the upper part of the case inside, due to the rotation of the crankshaft of the compressor. The oil is pumped upwardly, from the sump defined at the bottom of the case, through a discharge longitudinal channel provided in said shaft, then it is discharged through the upper end of said shaft and spread over all parts of the compressor which are located inside the case.
To join the parts of the muffler assembly, several known processes have been used nowadays, such as ultrasound or vibration welding processes, gluing processes and mechanic fixing processes using sealing gaskets.
The ultrasound or vibration welding processes are only useful to join the parts made of the same material and present the inconvenience of a certain instability to guarantee the tight attachment of the parts. This instability requires a control over 100% of the produced pieces, in order to evaluate the tightness of the assembled parts. Moreover, these processes include the costs of welding machines, accessories, frequent maintenance and spare parts.
The gluing processes, in which the parts are joined by means of adhesives, involve high processing costs since, considering the high producing rates and the profiles of the parts to be glued, the use of automatic devices for the application of adhesives is expensive and complex. Another inconvenience of these processes is that the parts must be completely clean in the region of adhesion, otherwise leakage will occur. This fact, added to the problems of adhesive application, require a control over 100% of the produced pieces.
It should also be considered that the adhesive to be used has to resist the conditions of the environment, such as refrigerant gas and oil under high temperatures. These parameters restrict the types of adhesives that can be applied, thereby increasing the cost of the adhesives in the process.
In the mechanic fixing systems using sealing gaskets, the parts are joined by means of mechanic fixing means, such as clamps or rivets and, between the parts, a sealing gasket made of rubber or asbestus is used. Thus, the muffler assembly assimilates the cost of a sealing gasket made of a material which should resist the aforesaid conditions of the environment.